Magnetoresistive apparatuses use magnetoresistive effects, in which a resistance changes depending on a magnetic field. Examples of such magnetoresistive effects are giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), anisotropic magnetoresistance (AMR) or colossal magnetoresistance (CMR). Bracketed together, these effects are also referred to as xMR. Therefore, magnetoresistive apparatuses may be used, in general, for measuring magnetic fields.
By way of example, such magnetoresistive apparatuses are used in speed, angle or rotational speed measuring apparatuses, in which magnets are moved relative to a magnetoresistive apparatus and hence the magnetic field at the location of the magnetoresistive apparatus changes in the case of movement, which, in turn, leads to a measurable change in resistance. By way of example, for the purposes of an angle sensor, a magnet or a magnet arrangement may be applied to a rotatable shaft and a magnetoresistive apparatus may be arranged stationary in relation thereto.
Magnetoresistive sensor elements of such magnetoresistive apparatuses typically comprise a plurality of layers, of which at least one layer is a reference layer with a reference magnetization. In some applications, a magnetoresistive apparatus in the process comprises a plurality of magnetoresistive sensor elements, which have different reference magnetizations. By way of example, such different reference magnetizations may be achieved by means of a laser magnetization. To this end, a region to be magnetized is exposed to a magnetic field corresponding to the desired magnetization, and a region to be magnetized is then heated by means of a laser beam. In this case, examples of such applications, in which various reference magnetizations are required, are angle sensors, compass sensors or specific types of speed sensors (for example, speed sensors in a bridge arrangement referred to as monocells).
Particularly in the case of small structures, the resulting magnetization in the case of laser magnetization is low when compared with a homogeneous magnetization process in a furnace; this is reflected in lower signal levels of a correspondingly implemented magnetic field sensor. Here, the lower magnetization may be caused, for example, by deflection of the laser beam at small structures, for example oblique structure flanks and the like. Here, this problem increases with decreasing structure dimensions, and so only insufficient magnetizations may be obtained for, in particular, small structure dimensions in sensor structures. On the other hand, samples can only be magnetized completely homogeneously in such a furnace, and different reference magnetizations in different regions on a substrate are not possible.
Therefore, it may be desirable to provide improved options for producing magnetoresistive apparatuses which comprise sensor elements with different reference magnetizations.